1. Field of the Invention
The present invention relates to methods for producing piezoelectric film actuators for use in, for example, liquid-ejecting heads.
2. Description of the Related Art
Known liquid-ejecting heads are disclosed in, for example, the following publications.    (1) Japanese Patent Laid-Open No. 2002-134806
According to this publication, a vibrating plate composite and piezoelectric films are provided to cavity parts by forming the piezoelectric films on an intermediate transfer member, bonding the vibrating plate composite to the piezoelectric films, and separating the intermediate transfer member to transfer the piezoelectric films to the vibrating plate composite.    (2) Japanese Patent Laid-Open No. 2002-234156
This publication discloses a piezoelectric element composite including a single-crystal or polycrystalline vibrating plate sandwiched between oxide layers and uniaxial-crystal or single-crystal piezoelectric films.
A liquid-ejecting head is provided by sequentially forming a SiO2 film, a YSZ film, Pt films, and PZT films, which function as piezoelectric films, on an SOI substrate, partially etching the Si substrate to form pressure chambers, and bonding an intermediate Si substrate and an orifice plate that constitute parts of the pressure chambers.    (3) Japanese Patent No. 2976479
This publication discloses a liquid-ejecting head including a nozzle substrate having nozzles, a silicon substrate having cavities communicating with the nozzles and thin film parts corresponding to the cavities, and pressure generators formed on the thin film parts integrally without any bonding step.    (4) Japanese Patent Laid-Open No. 10-286953
According to this publication, electrodes, lead-based dielectric layers, electrodes, and a vibrating plate are sequentially formed on a MgO substrate. After resin or glass for forming pressure chambers are provided on the vibrating plate, the MgO substrate is partially or completely removed. The pressure chambers are formed by, for example, patterning.
First Problem: According to Japanese Patent Laid-Open No. 2002-134806, after the piezoelectric films are transferred to the vibrating plate composite, a wiring step is required to provide, for example, electrical paths to the piezoelectric films. This step involves limitations such as the need for avoiding the breakage of ink cavities. Such limitations make it difficult to support flexibility in, for example, finer processing and heat processes.
Second Problem: The liquid-ejecting head according to Japanese Patent Laid-Open No. 2002-234156 has the following two problems.
(1) Use of an SOI Wafer leads to high production cost because the wafer is more expensive than general silicon wafers.
(2) If the selective etching of the Si wafer for forming pressure chambers is performed by alkali etching to ensure etching selectivity to the buried silicon oxide, the openings of the pressure chambers become larger than the areas thereof adjacent to the vibrating plate. This is disadvantageous in arranging the pressure chambers at higher density.
Third Problem: Japanese Patent No. 2976479 is disadvantageous in terms of the thickness control of the vibrating plate. As the amount of each droplet ejected is reduced to improve the resolution and gradation of ink jet printers, the number of ink dots per unit area on printing paper is increased. Accordingly, the responsiveness of the vibrating plate must be enhanced to maintain printing speed by, for example, reducing the thickness of the vibrating plate. The reduction in the thickness of the silicon vibrating plate, however, may cause a problem in thickness control because selective etching based on the difference in impurity concentration has low selectivity.
Fourth Problem: According to Japanese Patent Laid-Open No. 10-286953, the use of the MgO substrate makes it difficult to form peripheral circuitry, such as a drive circuit, using single-crystal silicon as an active layer. This is disadvantageous in terms of the finer processing of ink jet heads, which is accompanied by higher density. Because ink jet heads with higher densities require higher-speed drive circuits, it is desired to form peripheral circuitry on single-crystal silicon, which is a high-mobility material. If a Si substrate is used, however, the vibrating plate cannot be made of Si. This causes difficulty in achieving a high-quality single-crystal vibrating plate with good sensitivity.